Compressors screw-type

Screw-Type This type of rotary compressor, as shown in Fig. 10-80, is capable of hancmng capacities up to about 4.248 X lO" m m (25,000 fF/min) at pressure ratios of 4 1 and higher. Relatively small-diameter rotors allow rotative speeds of several thousand rev/min. Unhke the straight-lobe rotary machine, it has male and female rotors whose rotation causes the axial progression of successive sealed cavities. These machines are staged with intercoolers when such an... 

Figure 10-8. Screw-type rotary compressor. Courtesy of Dresser-Rand Company.)...

Figure 11-21A. Typical centrifugal compressor with economizer packaged refrigeration system. Note that screw-type or even reciprocating compressors can be used in such a system. (Used by permission Cat. 521-727, 1995. Carrier Corporation, a United Technologies Company.)...

Low-temperature, high-pressure gases at moderate to low temperatures can be expanded by the use of an expansion turbine (very similar to a steam turbine or even by reciprocating or screw-type compressors) or by the use of a throt-... 

Another important positive displacement compressor is the rotary compressor. This type of compressor is usually of rather simple construction, having no valves and being lightweight. These compressors are constructed to handle volumetric flowrates up to around 2,000 actual cfm and pressure ratios up to around 15 (see Figure 3-69). Rotary compressors are available in a variety of designs. The most widely used rotary compressors are sliding vane, rotary screw, rotary lobe, and liquid-piston. 

The lubrication requirements for single-screw type compressors are not severe, but in oil-flooded rotary units, the oxidizing conditions are extremely severe because fine droplets of oil are mixed intimately with hot compressed air. In some screw-type air compressors, the rotors are gear driven and do not make contact. In others, one rotor drives the other. The heaviest contact loads occur where power is transmitted from the female to the male rotor here the lubricant encounters physical conditions similar to those between mating gear teeth. This arduous combination of circumstances places a great demand on the chemical stability, and lubricating power, of the oil. 

LEYBOLD manufactures pumps such as the TURBOVAC 55 with an integrated Holweck stage (screw-type compressor) and, for example, the HY.CONE 60 or HYCONE 200 with an integrated Siegbahn stage (spiral compressor). The required backing pressure then amounts to a few mbar so that the backing pump is only required to compress from about 5 to 10 mbar to atmospheric pressure. A sectional view of a HY.CONE is shown in Fig. 2.52a. 

Rotary compressors are generally classified as of the straight-lobe type, screw type, sliding-vane type, and liquid-piston type. 

After a lively development in the past two decades during which positive-displacement screw-type and radial-turbo-compressors have replaced piston-type compressors in certain areas. The trend is now towards reciprocating compressors, again owing to their lower power consumption for many applications. 

Therefore, negative pressure was decreased to reduce tramp air. Also, the operational reciprocating compressor was replaced by a centrifugal rotary screw type compressor. Further, ash build up on the boiler superheater tubes was a problem, impeding heat transfer to cool down the flue gas. This problem was resolved by using acoustics to cause the ash to fall off the superheater and economizer tubes. This allowed lower fuel consumption, resulting in decreased NOx emissions.1... 

Compressors (low pressure, water injected, screw type) 340/hp 30... 

The pipeline transport of H2 requires compression. The electrolysis plant uses low pressure, water injected, screw type compressors to compress H2 from 1.02 bar to 8.0 bar to transport the H2 a short distance ( 10 miles) to a pipeline compression station. The energy to compress H2 from 1.02 bar to 8.0 bar is 1.37 kWh/kg of H2. There is no need for H2 storage at the electrolysis plant. At the pipeline compression station, the H2 is compressed from 8.0 bar to a pipeline pressure of 69.0 bar by high-pressure reciprocating compressors. The energy to compress H2 from 8.0 bar to a pipeline pressure of 69.0 bar is 1.17 kWh/kg of H2. PV electricity is used to power the compressors and water pumps at the compression station. 

It is ideal to have oil-fiw compressed air. Centrifugal machines generally are available up to 40,000 cfin. Oil free serew air compressors are available in smaller sizes. Regarding oil-free screw type compressors, it... 

Positive-displacement compressors, such as rotary lobe, screw type, or sliding-vane types, pump a relatively constant volume of vapor against whatever back pressure (resistance to heat transfer) is developed by the eveporator. The mass flow rate depends upon the inlet vapor density. Rotary lobe compressors are used for compression ratios up to about 2.0, the compression ratio being limited by mechanical and thermal distortion of small clearances inside the machine. The efficiency of positive-displacement compressors is between 60 and 75%. 

Table 8.2 lists the common failure modes of rotary-type, positive-displacement compressors. This type of compressor can be grouped into two types sliding vane and rotary screw. 

Technically, fans and blowers are two separate types of devices that have a similar function. However, the terms are often used interchangeably to mean any device that delivers a quantity of air or gas at a desired pressure. Differences between these two devices are their rotating elements and their discharge-pressure capabilities. Fluidi2ers are identical to single-stage, screw-type compressors or blowers. 

Fluidizers are identical to single-stage, screw-type compressors or blowers. They are designed to provide moderate- to high-pressure transfer of nonabrasive, dry materials. 

The example demonstrates that operating the compressor off the built-in pressure ratio means operating at a lower efficiency. This could be anticipated from Figure 4-3. The optimum port configuration for the various types of screw compressors was determined from a series of prototype tests. The change in volumetric efficiency is not a result of the built-in volume ratio, but is due to the increased slip (internal leak " n... 

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